Since Novikoff hepatoma ascites cells have 2 forms of uridine kinase which fluctuate in relative concentrations during chemotherapy and which have different kinetic parameters, changes in the uridine kinase isozymic profile will be monitored in a variety of animal tumors during chmotherapy with 5-fluorouridine (or 5-fluorouracil) 6-azauridine (or 6-azauracil) or 5-fluorocytosine. Attempts will then be made to relate to development of resistance in each instance to resulting changes in enzyme specificity. The kinetics of cellular uptake of the analogs will also be evaluated in view of recent results which indicate that transport may be modified in the resistant tumor cell. Further attempts will be made to determine whether the physiologically active glucocorticoid-binding protein i.e. the G-protein has adult and embryonic counter parts as does uridine kinase and many other eukaryotic proteins. Attempts will also be made to evaluate the significance of the macromolecular inhibitor for receptor-glucocorticoid transport which has been identified in several target tissues. BIBLIOGRAPHIC REFERENCES: yannarell, A., Schumm, D.E. and Webb, T.E. Nature of Facilitated Messenger RNA Transport from Isolated Nuclei. Biochem. J. 154: 379-385, 1976. Hanausek-Walaszek, M., Schumm, D.E. and Webb, T.E. The Repression and Derepression of Hepatic Tyrosine Transaminase by Carcinogens; Chemico-Biol. Interactions. 12: 391-396, 1976.